1. Field of Invention
This invention relates in general to a method of preventing overpolishing in a chemical-mechanical polishing operation. More specifically, the present invention relates to using a spin-on polymer material instead of a spin-on glass (SOG) material to prevent overpolishing in chemical-mechanical polishing operations.
2. Description of Related Art
Chemical-mechanical polishing is a universal technique which provides for global planarization of wafers in the semiconductor industry. The technique has gone through decades of improvements and is now successfully applied to all kinds of semiconductor products, such as microprocessors and memories.
A conventional planarization method is shown in FIGS. 1A and 1B. First, and referring to FIG. 1A, a planar surface 10, for example, a silicon substrate or an insulating layer having a pattern defined on a conducting layer 11 thereabove, is provided. The conducting layer 11 can be, for example, a polysilicon layer or a metallic layer. Then, an oxide layer 12 is formed above the surface of the conducting layer 11 using, for example, a plasma enhanced chemical vapor deposition (PECVD) method to form, for example, a silicon dioxide layer. Next, a spin-on glass layer 13 (for example, a kind of acidic silicon salt) is formed over the surface of the oxide layer 12. Thereafter, an oxide layer 14 is formed over the surface of the spin-on glass layer 13 using, for example, a plasma enhanced chemical vapor deposition method to form, for example, a silicon dioxide layer.
Referring next to FIG. 1B, a chemical-mechanical polishing operation is required oxide thickness level. In general, for a silicon dioxide layer formed using a plasma enhanced chemical vapor deposition method, the polishing rem oval rate is about 1500 .ANG. to about 6000 .ANG./minute using a chemical-mechanical polishing operation. In contrast, the acidic silicon salt type of spin-on glass has a polishing removal rate of about 3000 .ANG. to about 6000 .ANG./minute. When spin-on glass is used, only local planarization is obtained. This is because when a chemical-mechanical polishing operation is in progress, the spin-on glass layer 13 is reached after grinding away the full thickness of the oxide layer 14, because the oxide layer 14 just above the conducting layer 11 is thinner. As a result of the different polishing removal rate between the spin-on glass layer 13 and the oxide layer, the spin-on glass layer 13 and the oxide layer 12 above the conducting layer 11 will be completely removed with perhaps subsequent further grinding away of part of the top of the con ducting layer 11, causing damages to the components.